Mineral coated liquid-gas contact pad



EXAMINER 56 CEE-JSS REFERENCE Oct. 4, 1960 s. H. FRQHMADER MINERAL COATED LIQUID-GAS CONTACT PAD Filed June '7, 1957 limb .5V figa ,Afl

1 Mapli- 2,955,064 MINERAL COATED LIQUID-GAS CONTACT PAD Stanley H. Frohmader, Madison, Wis., assignor to Research Products Corporation, Madison, Wis., a corporation of Wisconsin Filed June 7, 1957, Ser. No. 664,231

14 Claims. (Cl. 154-46) This invention relates to means for providing large area contact surfaces for gases with liquids, and more particularly refers to an improved apparatus for cooling, filtering, humidifying, or dehumidifying gases, and for purifying or cooling liquids.

A variety of contact pads for use in gas-liquid contact apparatus have been disclosed in the art. They have been mainly composed of fibrous water-absorbent material such as animal or wood or vegetable fibers or superposed sheets of paper. One such contact pad is described in Patent No'. 2,637,540 and comprises a plurality of superposed sheets of high wet strength water-absorbent paper. Although many of these products have been satisfactory to a degree, they have all had some shortcomings. First, the fibrous water-absorbent material is soft and must be supported internally as well as externally by rigid frameworks. Second, upon continued. exposure to water the fibrous material loses its strength and eventually disintegrates. Third, there is a tendency for microorganisms to grow in the organic fibrous material, eventually causing decay to set in. This lowers its mechanical strength and often causes undesirable odors to be released into the air.

It is an object of the present invention to provide an improved apparatus for the ecient interfacial contact between a liquid and a gas.

It is a further object to provide a liquid-gas contact pad which presents to a flowing stream of gas a multiplicity of short, flat, wet baille surfaces disposed in such a manner as to provide eticient contact of the gas with the liquid carried upon the at surfaces.

It is a further object to provide a contact pad of the character described having a substantially rigid and selfsupporting structure and whose strength and rigidity is not affected by long continued contact exposure to the liquid used.

It is a further object to provide a contact pad of the nature described which in the preferred embodiment is free from organic material.

yIt is a further object to provide a contact pad whose surfaces carry a continuous inorganic coating providing efficient wicking action.

Other objects and advantages will become apparent from the follovn'ng description and drawings in which:

Fig. l is a perspective view of an embodiment of the gas-liquid contact pad in accordance with the present invention;

Fig. 2 is a perspective view of a small portion of one of the plurality of superposed sheets which together form a contact pad;

lFig. 3 is a cross-sectional view enlarged to show the contact junction between the baille elements of abutting sheets of contact pad, and

Fig. 4 is a vertical sectional view of a complete apparatus including the liquid-gas contact pad of the present invention.

'I'he complete evaporative apparatus shown in Fig. 4 includes a casing 1 which may be so shaped that itis Patented Oct. 4, 1550 adapted to lit into a window or other opening in a wall of the space to be cooled or humidied. The casing 1 has an inlet opening 2 in one wall and an outlet opening 3 in the opposite wall thereof. Means are provided for moving a stream of air through the apparatus, comprising, a fan 4 which is mounted inside the outlet opening 3 upon bracket 5 which is supported bythe casing 1. A protective grill 6 is mounted over the outlet opening 3 and fan 4. The fan 4 is adapted to draw a stream of air through the inlet opening 2 and forwardly through the casing 1 and out through the outlet opening 3.

A liquid-gas contact pad 7 is mounted within the casing and across the inlet opening 2. The contact pad is supported by a frame 8 arranged upon the rear wall of the casing 1 and borders the inlet opening along the bottom and two sides thereof. The frame has a flange 9 along the' inner edge thereof and the side and bottom marginal portions of the contact pad 7 fit into the frame with the edges resting along the main portion of the frame and the margin of the inner or outlet face resting against the flange 9. A frame-shaped retaining member 10 is hingedly supported at 11 upon the exterior of casing 1 and is adapted to rest in contact with the margin of the outer or inlet face of the contact pad 7. A spring latch 12 mounted on casing 1 releasably holds the pad-retaining member in the closed position. The contact pad 7 is removable and insertable into the frame 8 by swinging open-the retaining member 10 against the spring pressure of latch 12.

Means are provided for supplying` water to the top edge of the contact pad 7, comprising an elongated distributor 13 which is mounted within casing 1 immediately above the contact pad and. extends lengthwise of and is substantially coextensive with the top of the pad. 'I'he distributor 13 may be in the form of a pipe, as shown, and the lower portion of the Wall thereof is provided with a plurality of spaced openings 14 through which water is fed from the distributor 13 onto the edge of the contact pad. A pipe or hose, not shown, may be used to supply water to the distributor. 'I'he openings 14 are of such size and number as to feed a controlled quantity of water down upon the top edge of the contact pad 7, the water being distributed more or less uniformly over this area. The water flows downwardly and spreads through the body of the contact pad 7. Means are provided in the bottom of the casing 1 for removing the water that drips from the contact pad into the bottom of the casing. Such means comprise an opening 15 in the bottom wall of the casing to which is connected a .conduit 16, which may in turn be connected to a waste drain or else to a circulating pump (not shown) which may be connected to return the water to the distributor 13. The inlet to opening 1S may be protected by a stream 17, if desired, to prevent foreign matter from entering and clogging the pipe 16.

The contact pad 7 is illustrated separately in Fig. l. In accordance wit-h a preferred embodiment of the present invention, the pad comprises a plurality of superposed expanded sheets of a water resistant character. A fragment of an expanded sheet is shown in Fig. 2 and is formed in a known manner by cutting parallel lines of spaced-apart slits in a sheet, the slits of each line being in staggered relationship to those of the adjacent line,vand expanding the sheets in a direction transversely of the slits to convert the slitsinto openings. The expanded sheet is a network of thin, flat webs or baies 18 separated by the openings 19, the broad surfaces of the Webs being disposed at an oblique angle to the general plane of the sheet.

The sheets vare of a water resistant or Water-impermeable material to insure good adhesion between the sheets and the subsequently applied coating, the preferred material being aluminum foil, although other materials, such as other metal foils, plastic sheets, etc., may be used.

A plurality of the expanded sheets 20 are arranged in superposed relation to form a panel-like pad in which the planes of the sheets are parallel to the broad surfaces of the pad. The sheets are preferably arranged in such a manner that the openings of one sheet do not coincide with those of the next sheet, that is, the sheets are staggered so that the webs or battles of the sheets are in line with the openings between baffles of immediately adjacent sheets. Adjacent sheets may either all be oriented similarly or they may be oriented differently so that the long dimensions of the openings 19 extend in different directions in diterent sheets and the webs of adjacent sheets are non-parallel.

'Ihe sheets may be -fastened together by any of several methods. In one method, they may be united into a pad by stitching 21, which may -be applied in lines as shown in Fig. 1 by sewing a heavy thread through the thickness of the stack. Such uniting ofthe sheets holds the layers in close contact with each other so that the water can travel -from one sheet to another by a wicking action.

The superposed sheets vrnay also be united into -a pad by the methods disclosed in co-pending application Serial No. 630,591, filed December 26, 1956, for Filter and Method of Making the Same, which comprises, for example, dipping a group of sheets in a resinous adhesive and allowing the `adhesive to set after the excess has been removed. Additional methods may consist in yapplying the adhesive to spaced, localized areas of the assembly and subsequently heating the pads to cause the adhesive to drip down through the pad causing to bond the sheets to one another when the ladhesive cools.

The contact pads may initially be made in the form of an elongated blanket and rolled for storage purposes. The pads may then be cut from the blanket as desired.

In order to assure a rigid, rugged structure, the pad of superposed sheets may be faced on both of its broad surfaces with open-mesh, stiff, supporting grids 22 which are composed of an intersecting pattern of spaced apart wires or other stiff, elongated, non-absorbent members. The grids 22 are held in position by suitable means, such as wire hooks 24. The hooks are fastened at one end, as by welding or soldering, to one of the grids and pass through the body of the pad, and at the other end are looped about the members of the grids on the other side. The hooks are of such length that the grids are held firmly against the faces of the pads. The hooks, when properly applied, may'also serve to space the grids apart and protect the pad from being crushed during storage and shipment. Even greater rigidity may be provided by having pins or spikes att-ached 'to the grids and projection inwardly into the body of the pad. The spikes may be composed of metal and may be attached to the `grid by welding or any other suitable method.

In accordance with the present invention, the pads thus fabricated must next be provided with the mineral coating herein described. This coating composition is prepared by mixing together a slurry comprising (1) a finely divided mineral such as clay, carbonates, silicates and similar minerals, (2) a fibrous mineral such as asbestos, (3) a water-soluble silicate, and water. Additlonally, a strong base selected from the group consisting of ammonium hydroxide, sodium hydroxide, potassium hydroxide, and mixtures thereof, and a suitable wetting or dispersing agent, such as the sodium salt of a polymerized alkyl aryl sulfonic acid in the form of a powder, commercially available as Darvan No. l, may -beneicially be used, if desired. 'Ihe strong base aids both in making the coating more adherent to the metal base and 1n mcreaslng the porosity of the coating to improve the wicking action, and the wetting agent facilitates the mixing and application of the coating by aiding in the dispersion of the ingredients and in lowering 'the viscosity of the slurry.

After the slurry is prepared, the pads are immersed therein. After the pads are removed from the slurry they are vibrated or treated by any other suitable means to remove the excess coating. They are then dried either by the circulation of air, the Iapplication of heat, or by both methods together. During the drying, a reaction takes place between the silicate and the other ingredients transforming it to an insoluble hydrated silicate. Any excess unreacted silicate is subsequently Washed away during use. The dried, coated pads are then ready to be used as described above.

A fragment of expanded sheet is shown in Fig. 2 with a coating 23 covering the surfaces thereof. Where elements of two separate sheets are in contact, the coating bridges across them and assists the uniform transfer of the liquid from one sheet 'to another. Additionally, the bridging of the coating between the two sheets increases t-he rigidity of the pad. The bridging is shown by numeral 24 in Fig. 3 which shows, on enlarged scale, edges of two different expanded sheets in contact with each other.

The following examples are illustrative of the methods of preparing mineral compositions of the present invention and applying them to produce coated contact pads. Unless otherwise indicated compositions are shown in percentage by weight or in parts by weight.

EXAMPLE 1 Sixteen layers of slit and expanded aluminum foil 0.003 inch thick were superposed to form a pad 10" x 10 x 2". The layers were arranged with opposite orientation of adjacent sheets in order to prevent nesting of one within the other and provide tortuous, turbulenceproducing passages through the thickness of lthe pad. The pad was stitched together as shown in Fig. 1 using a four inch spacing. A grid support was then provided on each side as described above, the grids being tied at all corners to provide proper pad thickness.

'Ihe pad thus formed was then subjected to an etching bath in order to remove any oil adhering to the surfaces of the structure and to provide a roughened metal surface for the proper adhesion of the coating. This was accomplished by immersing the pad in a bath having the following composition:

Percent Caustic soda (76% NazO) 5 Sodium silicate (29% SiOg, 8.9% NazO) 1.0 Soft water 94.0

The pad was kept immersed for two to three minutes while the bath temperature was maintained a-t 25 C. It was then removed from the bath. The adhering dragout solution was allowed to remain on the pad.

A mineral coating composition was prepared having the following formula:

The wetting agent, soda, and sodium silicate were added to the water and mixed until a complete solution of all ingredients was obtained. The clay and asbestos were then added and mixing with good turnover was continued for about one hour or until the mixture became smooth.

All surfaces of all parts of the pad were then coated by immersing the pad in the mixture, raising ithe pad and lowering it several times while completely submerged in order to eliminate entrained air bubbles. Agitation of the coating bath was continued during the coating process in order to hold fthe viscosity of the mixture, which is thixotropic, at a reasonable level. The pad was then removed from the mixture. There was considerable bridging between the layers and considerable webbing across the holes of the mesh due to the fpresence of an excess of the coating composition. This excess material was removed by vibrating the coated pad, causing the excess material to ow down and drain away. This was continued until the pad had a wet coating weighing about one pound. Drying was accomplished by circulating air freely through the padl. Forced air either at room temperature or elevated temperature may be used; The dry coating had a weight of about- 140 grams. The pad' was then ready to beinstalled in anapparatus such as described above as shown in Fig; 4. When tested and compared' with the4 pad described' in Patent 2,637,540,

'the contact pad of ythepresent invention showedan. efli'- ciency improvement in water'- evaporation of 20%.

Table I below gives further examples wherein various minerals within the scope ofthe present invention were used for producing coatings. In all cases, satisfactory resultswere obtained when expanded metal pads were coated with the slurrys, prepared as indicated, produced from the minerals and subsequently dried according to they method of Example 1. However, the Peerless #l and Suprex clays gave superior results.

Each ofthe slurrys made had the following compositions:

A. The finely divided mineral shown g-.. 500

B. No. 7T-5 asbestos shorts g 500 C. The amount of soft water indicated in Table I.

D. The amount of sodium silicate indicated in Table I.

E. Darvan #l g l0 F. Caustic soda g Table I A C D Soit Sodium Finely Divided Mineral Water, Silicate,

gm. gm.

1. Peerless clay #1 [Hydrous aluminum silicate clay] 2,740 100.0 2.. Suprex clay [Hydrous aluminum silicate clayl-. 2, 740 100. 0 3. McNammce clay [Soit type white kaolln mlneral filler 1, 900 385.0 4. Pikes Peak washed clay 1, 947 385.0 6. Kaoiex D-6 [Air floated plastic kaolin particles1.- 1, 650 385. 0 6.* CCC Diluent [Calcium carbonate filler for rubber 1, 500 385.0 7. Dicalite l [Diatomaeeous silica] 2, 999 385.0 8. Zeolex 23 [Precipitated hydrated sodium silicol nlnminntpl 2, 914 385, 0 a. Attaelay WIP [Extender clay] 2, 684 385. o 10.' Attaclay 30160 [Extender clay] 3,162 385.0 11:..Silene EF liliydrated calcium silicate)- 3, 356 385.0 12.' D'olomite Natural occurring magnesium calcium carbonate] 2, G00 100. 0 13. China clay [High purit kaolin cla 2,000 100.0 14. Asbestos Powder 2,000 100.0 15. Tale powder 2,000 100.0 16. Mica [27 mesh 2,000 100.0 17. Permage- [Hy rated magnesium aluminum silicate 2,740 100.0 18. Zeolite lines [Hydrated sodium aluminum um i h m 3,140 100 0 19. Santocel ARD [Light we g t, porous s ca aerogel] 6, 666 100. 0

Other finely divided minerals may be used, among them are -alkaline earth metal silicates such as calcium silicate, and'alkaline earth metal carbonates such as calcium carbonate. Other mineral fibers which may be used include rock wool and glass fiber.

The relative proportions of the iinely divided mineral, are not critical. In general, as the relative amount of clay is raised, the adhesion of the dried coating to the supporting base improves but the wicking properties decline, and as the ratio of asbestos to clay is increased, the wick-ing properties improve but the adhesion declines. Additionally, as the proportion of either component is increased above 50%, the viscosity of the coating mixture increases materially. It is possible to obtain satisfactory coatings using mixtures falling within the range fromz about 10 parts tinely divided mineral to 90 pants mineral liber by weight to a ratio of 90 parts finely divided: mineral to l0 parts mineral liber by weight. The preferred proportions lie in the range of from 75-25 to 25-75. Optimum results are obtained in the range from -40 to 40-60.

Among Ithe 'silicates which may be used are sodium silicate and potassium silicate. The amount used is not critical and in general may vary from about 50 grams to about 500 grams for each thousand grams of mixture of finely divided mineral and mineral fiber. Stated in terms of SiO2 content, the ratio by weight of the SiO', content to the total of nelydivided mineral and mineral fiber must be at least' 1.45z100. This ratio is obtained by multiplying the 29% value of the SiO2 content off the sodium silicate solution listed above times the 50 grams SiOg, per thousand grams total mixture referred to immediately above. The soluble silicates promote the setting of the coating and improve adhesion.

Although not indispensable, it is desirable toadd a small amount of a strong base such as sodium hydroxide. This'- appears to improve the porosity of the coating on the foil because of its etching or corroding action. Sodium hydroxide, potassium hydroxide, or any other strong water-soluble hydroxide which will not form precipitates with the silicate may be used. The preferred amount of strong base is about 10 grams per thousand grams of a mixture of iinely divided mineral and mineral bers.

The coated contact pads herein disclosed have many advantages over those of the prior art. They are highly effective for the purpose of bringing a large surface of water into contact with the air for producing rapid evaporation thereinto. The pads are very pervious and oier but little resistance to the flow of air. Being composed of interstitial networks of thin, fiat, narrow webs which lhave their broad, flat surfaces disposed at oblique angles to the general direction of flow of air through the pads, turbulence at the very extensive surfaces provides efficient wiping action to continuously pick up and carry away the moistureladen air at the interface. The surface coatings of these webs are continuously soaked and by a wicking action in the coating the water is caused to spread uniformly throughout the total coating contained on the surfaces of the layers. The coating of the webs carries water throughout the surfaces of all parts of the pad area and each web serves as a small baille which deflects the liowing stream of air. As the water is continuously carried away, it is replenished by migration from other portions of the unit upon the surfaces of the network by the wicking action of the mineral coating to keep all surfaces uniformly wet. The expanded pattern provides a uniform porosity throughout the area of the unit and air is brought into thorough, uniform contact with the liquid throughout the body of the pad.

The coatings exhibit an additional desirable property which is entirely unexpected. As normally operated, water is fed to the pads at such a rate that about 25% of the water evaporates and the rest is carried away to a. drain. It has been found that when a moderately hard water is used, only 2% of the minerals contained in the 25% water which is evaporated will settle out on the surface of the pad while the rest of the minerals are removed by the excess water. This is in contrast to the results obtained in using the organic type pads of the prior art where much larger percentages of the minerals are retained on the pad.

Another advantage of the present liquid-gas contact pad, demonstrated by extensive testing, is that the gradual deterioration in performance caused by the accumulation of scale deposits is not as great as with other types of evaporation media, such as those made of massed fibers or filaments. Also, the open and uniform porosity of the unit results in its maintaining its effectiveness and low resistance to air ow over a long period of use. It has been found, furthermore, that a contact pad constructed as described herein resists rupture and disintegration and has a long useful life. It is relatively simple 7 in structure and is inexpensive to manufacture and use. Because it is comprised, in its preferred form, of metallic foil containing a mineral coating, it is fire-proof. This feature is especially desirable where the element is to be used in conjunction with a heating plant for humidifying heated air.

Although the invention has been described in relation to the use of expanded metal as the supporting medium, various other types of reticulated bodies may also be used.

By Way of definition, the term expanded as used in the specification and claims herein means the slitted and expanded condition such as has been described in connection with the sheet illustrated in Fig. 2. Additionally, the term air is intended to include other gases which it may-be desirable to cool, humidity, or for any other purpose to bring into intimate contact with continuously wetted surfaces.

Although the liquid-gas contact pad of the present invention has been described mainly in its relation to the evaporation of a liquid into air, it has also proven to be extremely effective and very unexpectedly so as an air filter for the removal of micro-organisms. Table II, below, shows the results obtained in ltests for eiciency in this service. The tests were made using both the mineral coated evaporative pad of the present invention and filters presently available on the market. In each case a pad or iilter element 10" x 10" x 2" was used and an air velocity of 350 feet per minute maintained. Element Nos. l and 2 were commercial air lters available on the market. Element No. 3 was a commercial paper-type element used for humidifying and cooling air. Element No. 4 was a commercial water cooling pad composed of aspen excelsior. Element No. 5 was the mineral-coated aluminum foil pad of the present invention. In the case of pads 3, 4 and 5, water was introduced at the rate of 3 gallons per hour, pads 1 and 2 being dry. Apparatus and methods commonly used in the art were used for the tests.

l Not measured.

The results of the tests illustrate that the efciency in removing micro-organisms is extremely high in the case of thewet mineral-coated evaporative element of the present invention, more than twice as high as the nearest competitive type of filter.

The contact pads of the present invention may be used for many purposes. First, they may be used to evaporate water into the air in order to raise the relative humidity as described above. Second, the pads may be used to evaporate water into the air in order to lower its temperature, as for room air conditioning. Third, the pad may be used to remove moisture from the air by introducing a hygroscopic liquid such as a solution of lithium chloride or ethylene glycol into the pad instead of water. The liquid absorbs the moisture from the air as the air passes through the pad. The liquid is subsequently removed from the pad together with the water, and the excess water removed for reuse of the hygroscopic liquid. As also disclosed above, the pads may be used Ito remove particles such as dust and micro-organisms from the air.

The present contact pad may also be used for the treatment of a liquid which is ilowed over its surfaces as air or other gas is blown through the pad, rather than oxidize organic matter contained in the water.

i 8 for treatment of the air. Thus, industrial process water may be passed over the element in order to cool 4it by exposure to -a stream of air. Or, water may be aerated by passing it through the pad while a current of air through the pad is maintained. This eliminates undesirable gases such as hydrogen sulde and odors and may The contact pad may also be used for the aeration of sewage. As a result the various nitrites contained are oxidized by the air to nitrates.

Other variations of the present invention will occur to those skilled in the art from a reading of the above disclosure, but such variations are to be considered as being within the spirit and scope of the invention as dened by the following claims. A A

I claim:

l. A gas-pervious liquid-gas contact pad comprising a reticulate body of water-impermeable material having a large area of surfaces exposed, said surfaces having wicking coatings thereon, said coatings consisting essentially of (1) a finely divided mineral, (2) mineral fibers, and (3) a water-soluble silicate, the ratio by weight of (l) to (2) being from about 10:90 to about 90:10, and the ratio by weight of the Si02 content of (3) to the total of (1) plus (2) being at least 1.45:100. f

2. A gas-pervious liquid-gas contact pad comprising a plurality of superposed rsheets of a water-impermeable material, said sheets each comprising a substantially uniform open-mesh network having a large area of exposed surfaces, said surfaces having substantially continuous wicking coatings thereon, said coatings being substantially continuous throughout the area of each said sheet and consisting essentially of (1) a nely divided min eral, (2) mineral fibers, and (3) a Water-soluble silicate, the ratio by weight of (1) to (2) being from about 10:90 to about :10, and the ratio by weight of the SiOz content of (3) to the total of (l) plus (2) being at least 1.45 :100.

3. A gas-pervious liquid-gas contact pad comprising a plurality of superposed sheets of a water-impermeable material, each of said sheets comprising an open-mesh network of interconnected thin fiat webs having their broad surfaces disposed at an angle to the general plane of the sheets, the surfaces of said webs having wicking coatings thereon, said coatings being substantially continuous throughout the area of each said sheet and consisting essentially of (1) a finely divided mineral, (2) mineral bers, and (3) a water-soluble alkaline metal silicate, the ratio by weight of (1) to (2) being from about 10:90 to about 90: 10, and the ratio by weight of the SiO, content of (3) to the total of (1) plus (2) being at least 1.45 :100.

4. A contact pad in accordance with claim 3 wherein the wicking coatings of the several sheets are interconnected with coatings of adjacent sheets whereby said coatings are substantially continuous throughout the pad.

5. A contact pad according to claim 3 wherein said coating includes a water soluble hydroxide of a monovalent cation.

6. A contact pad according to claim 3 wherein said iinely divided mineral is clay.

7. A contact pad according to claim 3 wherein said iinely divided mineral is clay and said mineral ber is asbestos fiber.

8. A contact pad according to claim 3 wherein said coating comprises clay, asbestos fiber, sodium silicate, and sodium hydroxide.

9. A contact pad according to claim 3 wherein said nely divided mineral is a silicate of an alkaline earth metal.

10. A contact pad according to claim 3 wherein said finely divided mineral is a carbonate of an alkaline earth metal.

11. A gas-pervious liquid-gas contact pad comprisin a plurality of superposed layers of expanded aluminum foil, substantially all surfaces of said foil having a wicking coating thereon, :said coating consisting essentially of (1) a finely divided mineral, (2) mineral fibers, and (3) a water-soluble alkali metal silicate, the ratio by weight of (1) to (2) being from about 10:90 to about 90:10, and the ratio by weight of the SiOz content of (3) to the total of (l) plus (2) being at least 1.45: 100.

12. A process for providing a substantially continuous adherent mineral wicking coating upon the surfaces of a water-impermeable body of reticulate structure comprising mixing together a composition consisting essentially of (1) a nely divided mineral, (2) mineral fibers, (3) a water-soluble alkali metal silicate, and (4) water, the ratio by weight of (l) to (2) being from about 10:90 to about 90:10, and the ratio by weight of the'SiOz content of (3) to the total of (1) plus (2) being at least 1.45 :100; applying the mineral composition to the surfaces of said body, and removing the water by evaporation.

13. A process for providing a substantially continuous adherent mineral wicking coating upon the surfaces of a water-impermeable body of reticulate structure comprising mixing together a composition consisting essentially of (1) a nely divided mineral, (2) mineral fibers, (3) a. water-soluble alkali metal silicate, (4) a water-soluble hydroxide of a monovalent cation, and (5) water, the ratio by weight of (l) to (2) being from about 10:90 to. about 10, and the ratio by weight of the Si02 content of (3) to the total of (l) plus (2) being at least 1.45:100; applying the mineral composition to the surfaces of said body, and removing the water by evaporation.

14. A process according to claim 13 wherein said composition is comprised of (1) clay, (2) asbestos bers, 3) sodium silicate, (4) sodium hydroxide, and (5) water.

References Cited in the iile of this patent UNITED STATES PATENTS 322,307 Merritt July 14, 1885 344,409 Schimmelpfeng June 29, 1886 389,210 Faure Sept. 11,- 1888 406,563 Catlin July 9, 1889 1,598,644 Greene Sept. 7, 1926 2,095,451 Reynolds Oct. 12, 1937 2,121,278 Babcock June 2l, 1938 2,349,909 Meharg May 30, 1944 2,509,599 Hollenberg May 30, 1950 2,610,893 Collins et al Sept. 16, 1952 2,637,540 Rowe May 5, 1953 L* r q 

3. A GAS-PERVIOUS LIQUID-GAS CONTACT PAD COMPRISING A PLURALITY OF SUPERPOSED SHEETS OF A WATER-IMPERMEABLE MATERIAL, EACH OF SAID SHEETS COMPRISING AN OPEN-MESH NETWORK OF INTERCONNECTED THIN FLAT WEBS HAVING THEIR BROAD SURFACES DISPOSED AT AN ANGLE TO THE GENERAL PLANE OF THE SHEETS, THE SURFACES OF SAID WEBS HAVING WICKING COATINGS THEREON, SAID COATINGS BEING SUBSTANTIALLY CONTINUOUS THROUGHOUT THE AREA OF EACH SAID SHEET AND CONSISTING ESSENTIALLY OF (1) A FINELY DIVIDED MINERAL, (2) MINERAL FIBERS, AND (3) A WATER-SOLUBLE ALKALINE METAL SILICATE, THE RATIO BY WEIGHT OF (1) TO (2) BEING FROM ABOUT 10:90 TO ABOUT 90:10, AND THE RATIO BY WEIGHT OF THE SIO2 CONTENT OF (3) TO THE TOTAL OF (1) PLUS (2) BEING AT LEAST 1.45:100. 